The invention relates to a method of producing a vehicle steering wheel.
Vehicle steering wheels are often structured in such a way that a metallic skeleton, which forms a base element for the steering wheel rim, spokes and hub, is surrounded by one or more foamed or injection-molded plastic layers. The skeleton provides the necessary stability for the steering wheel, while the plastic layers account for the appearance and feel of the finished steering wheel. In order to reduce the weight as well as to simplify the production method and thus to cut costs, attempts have been made to replace the skeleton with plastic components whenever possible. German utility model DE 299 01 404, for example, describes a steering wheel, the steering wheel rim of which is made completely of a fiber-reinforced plastic. Although this steering wheel achieves a considerable weight reduction while maintaining excellent stability, there is still a problem, namely, the fact that the steering wheel rim has to be reworked in order to ensure that no reinforcement fibers protrude beyond its surface, which would have a negative impact on the tactile comfort.
The present invention proposes a method of producing a vehicle steering wheel which, while maintaining the advantage of using a stable carrier component, can lower the production costs in comparison to the prior-art process.
According to the invention, a method of producing a vehicle steering wheel including a steering wheel rim comprises the following steps: A foaming mold with a top part and a bottom part is used; two different foam components, namely, a central carrier component as well as a soft component surrounding the latter, are injected into the bottom part which is not closed by the top part; the foaming mold is closed by closing the bottom part with the top part, and; the foaming mold is heated. In this manner, one production step suffices to manufacture the load-bearing component of the steering wheel as well as the component that surrounds it and that offers considerable tactile comfort. The introduction of the various components is facilitated by the open foaming mold. Only after the mold has been closed, the foaming procedure takes place in which the plastic layers of the steering wheel acquire their final shape by means of the application of heat. Since the central carrier component is surrounded by the soft component, reworking the surface of the carrier component is not necessary. Moreover, the normally hard carrier component is covered by a soft component with a more pleasant feel.
Preferably, the central carrier component is surrounded by the soft component on all sides in order to ensure a high level of tactile comfort everywhere on the steering wheel.
The central carrier component can be a rigid foam or a fiber-reinforced foam, with the possibility of using familiar materials such as for example, fiberglass or Kevlar-reinforced foams of the type described in German utility model DE 299 01 404.
Advantageously, at least the steering wheel rim can be made up exclusively of the carrier component and the soft component. It is also possible to manufacture the spokes in this manner. Therefore, the steering wheel skeleton can be reduced to a minimum.
In a preferred embodiment of the invention, a nozzle is used to introduce the components into the bottom part, said nozzle having a central outlet for the carrier component and an annular outlet for the soft component surrounding the central outlet. When such a nozzle is used, both components are introduced into the foaming mold in their desired arrangement at the same time so that the production time can be kept to a minimum.
As an alternative, first a bottom layer of soft component material can be introduced into the bottom part, subsequently the carrier component can be applied in a middle section of the bottom layer, and finally, once again, the soft component material can be applied such that the carrier component is surrounded by the soft component. In this case as well, after the completion of the production process, the carrier component is completely surrounded by the soft component. Here, the nozzle for introducing the components does not need to have a complicated configuration.
In this version of the process, the same nozzle can be used for introducing the carrier component and the soft component, or else two different nozzles can be used.
The nozzle is preferably operated by a robot. Among other things, this makes it easier to adapt the method to different steering wheel geometries.
Additional features and advantages of the invention will be apparent from the description below of two embodiments.